第一个正在用,感觉挺不错的

Office Ribbon Project
http://windowsribbon.codeplex.com/

Qios Devsuite
http://www.qiosdevsuite.com/
http://blogs.microsoft.co.il/blogs/arik/image_thumb_4B88231F.png
Windows Ribbon for WinForms
http://windowsribbon.codeplex.com/
另外补充几个在用的其他插件
日历插件

Another Month Calendar
http://www.codeproject.com/Articles/10840/Another-Month-Calendar
控件动画

Animator for WinForms
http://www.codeproject.com/Articles/548769/Animator-for-WinForms